Problem: $ { {3} \times \left[\begin{array}{rr}{3} & {4} \\ {-1} & {-1} \\ {1} & {-2}\end{array}\right] = {?} } $
Solution: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{3}\times{3} & {3}\times{4} \\ {3}\times{-1} & {3}\times{-1} \\ {3}\times{1} & {3}\times{-2}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{9} & {12} \\ {-3} & {-3} \\ {3} & {-6}\end{array}\right]}$